1. Field of the Invention
The present invention relates to an ink jet head in which part of drive circuits are incorporated, a substrate for the head, and an apparatus provided with the head. In the specification and claims, "recording" includes ink application etc. (printing) onto any ink supporting member to which ink is to be applied, such as fabric, thread, paper, sheet medium, etc., and "recording apparatus" includes all types of information processing apparatus and printers as an output device thereof. Therefore, the present invention can be applicable to applications in these fields.
2. Related Background Art
An example of a recording head unit in an apparatus applied to the liquid jet recording method, as described in Japanese Laid-open Patent Application No. 54-51837, German Laid-open Patent Application (DOLS) No. 2843064, etc., is provided with orifices (discharging openings) arranged to discharge a liquid (ink); liquid discharging portions communicating with the respective orifices and having respective liquid paths (channels) each comprising as a part of structure a thermal action portion in which thermal energy to be utilized for discharging the liquid in the form of drop acts on the liquid; and electrothermal converters as means for generating the thermal energy.
An electrothermal converter has a pair of electrodes and a heating resistor layer connected to the electrodes and having a heating region (heat generating portion) between the electrodes. The pair of electrodes are generally composed of a select electrode and a common electrode in such an arrangement that with current supply between the electrodes the heat generating portion generates the thermal energy utilized for discharging the liquid through an orifice as described above.
The conventional recording heads were constructed in such an arrangement that an array of electrothermal converters were formed on a monocrystal silicon base while functional devices for driving the electrothermal converters, for example an array of transistors, were provided as drive circuits for the electrothermal converters outside the silicon base and that flexible cables or wire bonding etc. was used for connection between the electrothermal converters and the transistor array.
In order to simplify the structure considered for the above head arrangement, to reduce defects produced in fabrication steps, to make performance of devices consistent, and to improve reproducibility, there is a known ink jet recording apparatus having a recording head in such an arrangement that electrothermal converters and functional devices are provided on a same base, as described in Japanese Laid-open Patent Application No. 57-72867 corresponding to U.S. Pat. No. 4,429,321.
FIG. 1 is a cross-sectional view to show a part of a substrate for recording head in the above arrangement. Reference numeral 301 designates a * semiconductor supporting member of monocrystalline silicon. Further, 302 denotes an epitaxial region of n-type semiconductor, 314 an ohmic contact region of n-type semiconductor of high impurity concentration, 313 a base region of p-type semiconductor, and 305 an emitter region of n-type semiconductor of high impurity concentration, thereby forming a bipolar transistor 315. In addition, 306, 308 are silicon oxide layers as a heat storage layer and an interlayer insulating layer, 310 a heat resistor layer, 309 a wiring electrode of aluminum (Al), and 311 a silicon oxide layer as a protective layer, thereby forming a substrate 316 for recording head. Here, the heat resistor layer 310 becomes a heating portion. Then liquid paths (channels) are formed on this substrate 316 so as to construct a recording head.
Such an ink jet recording head, particularly an ink jet recording head utilizing foaming of ink with heating of heater, uses p-n junction diodes, bipolar transistors, or MOS transistors for switching of current. These semiconductor devices are normally made of monocrystalline silicon.
FIGS. 2A to 2C are drawings to show a p-n junction diode of monocrystalline silicon in a conventional example, wherein FIG. 2A is a cross section and FIGS. 2B and 2C are equivalent circuit diagrams. In FIGS. 2A to 2C, an aluminum wire 2a shorts the circuit between the base and the collector of bipolar transistor, whereby the transistor operates as a p-n junction diode. The reason why the bipolar transistor is used as a p-n junction diode is to prevent interference between adjacent transistors by device isolation, thereby preventing latchup. Also, a drive current can be set high by transistor operation.
The above conventional examples, however, had the following two drawbacks because p-n isolation was employed for electrical isolation of diodes.
(1) A parasitic bipolar transistor is formed among the base portion 313 and collector portions 303, 304 of diode, and the supporting members 301, 302. In order to stop a current flowing into the supporting members 301, 302, the collector portions 303, 304 of diode, i.e., the base portion of the parasitic bipolar transistor needs to be a high concentration layer. Thus, a spread in length and width of the diffusion layers 303, 304 becomes larger, which is a factor to obstruct miniaturization of diode.
(2) Since the base region 313 needs to be three-dimensionally junction-isolated, existence of the buried layer 303 becomes essential, so that the fabrication steps must include epitaxial growth. The epitaxial growth step becomes a factor to considerably raise the production costs in fabricating cheap ink jet heads, resulting in increasing the costs of manufacture.
Plainly speaking, the above conventional examples had the following problems because they used monocrystalline silicon.
(1) The supporting member used is expensive.
(2) A high-temperature process is required.
(3) A large device isolation region is necessary.
(4) Device performance becomes over specifications.